Steel doors are usually formed with edge parts or channels. The face plates or panel members of the door are secured by fasteners, such as rivets or screws, or by spot welds. By constructing the metal door in this manner, the door must be painted after completing construction to cover the fasteners, welds and other structural parts. Because of the conventional connection of the various parts, pre-coated or pre-painted steel metal cannot be employed.
To avoid these problems and to manufacture a door without the use of fasteners or welding, doors with couplings along the side edges have been proposed. Examples of such doors are disclosed in U.S. Pat. Nos. 4,819,383 and 4,896,458 to McKann et al, the subject matters of which are hereby incorporated by reference.
Since the interior of these doors merely include insulating core members located between the panels, the inner panels can be marred by denting the relatively thin steel material forming the door panels. Thus, the doors need to be reinforced to avoid this denting problem.